Shielded spark plug



July 27, 194s. L. F. HAHN SHIELDED .SPARK PLUG Filed Aug. lso, 1943 ATTORNEY Patented July 27, 1948 UNITED STATES PATENT oEFIcE smELDED SPARK PLUG Lewis F. Hahn, Hatboro, Pa.

Application August 30, 1943, Serial No. 500,537

The invention relates in general .to a spark plug, specifically to the unit which includes the shell and core assembly of a spark plug of the shielded type, and the invention also relates to a method and apparatus for fabricating the same. The present disclosure constitutes a development and in some respects an improvement over the form of spark plug disclosed in mycopending application Serial No.'383,725 filed March 17, 1941 entitled "Shielded spark plugs", which became forfeited but was reled under Serial No. 712,227, filed November 25, 1946.

In the previous application there was featured a form of spark plug in which among other things a .gasket of soft metal was located between the conical portions of the core assembly' and the shell element of the spark plug. This metal' gasket possessed two functions; it was designed to be rotated to provide for an adjustment ofthe spark plug firing gap, and was also designed to provide for a controlled conduction of heat from the'core assembly to the shell by the replacement of one gasket for another of different length.

The present disclosure like that in the pending application likewise features the utilization of such a gasket to provide for the requisite area of heat transference between the core assembly and th'e shell in addition to its usual function of forming a gasket between the core assembly and shell. Rather than to provide for possible adiustments of the parts of the spark plug while in use as featured in the prior application, it is preferable under some circumstances and, incidentally, more economical to provide a form of spark plug which does not provide such refinements as means for varying the spark gap setting or for varying the rate of heat transference but in which the component parts are accurately preset and fixed in place in the factory during the course of manufacturing the same so as to meet the normal or usual operative conditions and to thus use them for the life required of such spark plugs under aeroplane flying conditions. It is the intent in so far as the present disclosure is concerned to make the spark plugs so cheaply that they can be thrown away after their maximum period of service has been attained.

Accordingly, the primary object of the invention is to provide a simple form of spark plug in which the component parts are permanently and securely preset in the position in which they are intended to occupy in the finished article and in this way defeat any possibility of the inexperienced operator changing th'e spark gap or the heat conducting features after the component parts 4 Claims. (Cl. 123-169) 2 have been once accurately set in the process of fabricating the plugs.

Still another object of the invention is to 'provide a form of spark plug which will feature nonleakage past the core assembly of the high pressure gas generated in the firing chambers of the internal combustion engines of th'e aeroplane type now in general use.

With reference to the method aspect of the disclosure an object of the invention is to provide a simplified technique and by the use of powerful die presses of suiiicient power to assemble the component parts accurately -in their prefixed relation even to the extent of distorting the parts, to provide for the necessary gas tight fit and permanency of assembly.

Various other objects and advantages of the invention will be in part obvious from a consideration of the method features of th'e disclosure and from an inspection of the accompanying drawings and in part will be more fully set forth in the following particular description of one method of practicing the invention, and the invention also consists in certain new and novel modifications oi' the preferred method and other features of construction and combination of parts hereinafter set forth and claimed.

In the accompanying drawing:

Fig. 1 is an axial sectional view taken through a spark plug constituting a preferred embodiment of the article aspect of thedisclosure showing the same mounted on an engine cylinder;

Figs. 2 and 3 are each vertical sectional views of the spark plug showing two succeeding steps in its fabrication and illustrated in connection with the die press apparatus for performing the step; Fig. 2 showing the means for securing the core assembly to the shell and Fig. 3 showing the means for securing a spacing sleeve to the shell and for curling the upper end of the shell into binding engagement with the shielding barrel of the spark plug; and

Fig. 4 is an axial sectional view ot' the upper portion of a modified form of shell.

Referring rst to the disclosure in Fig. 1, there is shown the wall A of the head of an internal combustion engine provided with a spark plug opening B. The inner surface of the wall A is shown at C and the outer surface at D. Spark plug I0 is screwedv into the opening B preferably until its inner end I I is flush with the inner surface C of the wall A. The spark plug includes three major elements, a shell I2, a core assembly I3 a'nd a metallic shielding barrel I4. The shell I2 is formed with a cylindrical lower porasentar tion iii, and an enlarged heir portion ifi; and is reduced at its upper extreme edge to forma thin annular fastening flange il' initially upstanding as shown in Fig. 2. Between the hex portion it and the cylindrical portion lil there is formed an overhanging shoulder i8. Between this shoulder and the threads la on the lower portion is a smooth cylindrical bearing portion 2t. A spacing sleeve 2l for locating the terminals at the inner surface C snugly embraces the bearing portion 2c and is'in nrm bearing engagement with the shoulder it. A .soft metal washer 22 is squeezed between the lower end of the sleeve 2i and the outer surface D of the cylinder wall. A bore 23 extends axially through the shell with the upper portion 2li thereof that is, 'the portion encircled by the hei; nut it being cylindrical and of relatively large diameter. "She lower portion 2li of the bore is cylindrical with a diameter slightly less than the diameter of 'the upper por tion 26. The extreme lower end oi the bore is constricted by an integral annular flange 2li which forms the outer electrode of the spark Plug.

The core assembly i3 includes a ceramic body portion 2l, the lower part 28 of which is conical, the upper part 29 of which is cylindrical and which is provided therebetween with an outstanding Iiange or shoulder dil. The body portion 2l is provided with a smooth bore di extending axially therethrough from end to end. The upper face of the shoulder @il is curved downwardly and outwardly and it is the intent that the portion of the flange which is engaged by the lower end of the shielding barrel ll shall accurately denne a horizontal plane c-d at right angles to the axis of the spark plug indicated by the rnedial lines a-b.' y

A. soft metal gasket 32, preferably formed of copper, is located between the conical lower portion 28 and the gasket 'seat 33 formed in the bore of the shell between the cylindrical end portions. In the illustrated instance, the gasket seat is long and has an inclination to the axis of the shell of the order of five degrees This gasket 32 is of truste-conical form, its cross section of material is substantially the same from end to end and preferably is extremely thin in order to facilitate its distortion as hereinafter described. 'I'he showing of thickness in the drawings is exaggerated The core assembly includes a spindle 34 provided at its lower end with an enlarged head 35 which is centered within the external electrode 26 and forms the inner electrode of the spark plug. The shank 36 of the spindle extends through the bore 3i and has its upper end threaded as shown at 3l. 'A distortable gasket 38 is located in a pocket formed between the upper end of the body portion and a nut im which engages the threads at 3l as more fully described in copending application entitled Spark plug gasket, filed herewith.

The shielding barrel i4 is of tubular form externally threaded at its upper end 4i for engagement conventionally with the lead-in cable (not shown) for supplying the spark plug with electric energy. The upper end of the barrel has a locking rim 42 integral therewith and turned into the bore of the barrel but otherwise the bore of the barrel is of uniform diameter from end to end and its lower end is wide open. A preformed sleeve 43 of insulating material forms a lining for the barrel and forms therein and above the core assembly a pocket 44 for receiving therein the intruded end of the conductor lill ' of the spindle.

'which supplies electric energy to the upper end The sleeve is slipped into the barrel from its inner wide open end and ad vanced until it engages snugly against the locking rim CS2.

The lower end of the barrel is thickened to provide a long, outstanding, cylindrical bushing 'd5 contained in the upper portion it oi the shell.

The bearing provides a bevelled bearing shoulder it at its upper side. The extreme lower end of the shielded barrel is recessed to fit the curvature of the upper face of the flange or shoulder mi in the plane thereof indicated by line c-d. The fastening flange il is bent, pressed or rolled from its upstanding position shown in Fig. 2 inward into bearing engagement with the shoulder iti as shown in Figs. l and 3 to force the bushing and with it both the barrel and its lining downwardly into snug engagement with the shoulder til oi? the body portion.

`With reference to the manner in which the device of Fig. i is formed, it will be understood that the parts are subjected to die press operations. Reference is made nrst to the showing in Fig. 2 which illustrates die press apparatus for locking the core assembly permanently to the shell. The die press apparatus includes bed plate @ll of a power press, the rarn of which is shown at (la. Mounted on the bed plate is a gap setting gauge die. This is simply ablock provided centrally thereof `with an upstanding ring t@ and the surface of the block outside of the ring provides a at bearing surface 5l. rl'he ring a@ is carefully dimensioned in its width of material to define the spark gap 52 desired in the finally finished spark plug. Depending from the press ram le is *a hollow plunger 53 provided with a recess ed of sufficient diameter to contain the upper portion 29 of the core assembly. The lower edge 5a of the plunger 53 is contoured Ato flt the upper face of the flange 3u around the part thereof defined by the plane c-d.

In operation the core assembly ifi is mounted in the shell with the gasket 32 therebetween approximately in the position in which these parts will eventually be located Iin the nished article. The parts are so proportioned that initially, that is. when the parts have been pressed together by simple manual operation, 'the inner electrode 35 will be 'spaced inwardly above the position which it will eventually occupy and intruded slightly into the guiding ring Ell.' It is understood lat this time that the gasket 32 has a fairly snug .fit against the ysurfaces engaged thereby, that is, as sn-ug as can be attained by manual insertion of the core assembly into position. The ram 48 and plunger 53 are then lowered to bring the plunger into position telescoping the upper portion of the core assembly, intruding into the upper open end of the shell and enga-ging the outf standing flange 3@ as shown in Fig. 2. It will be noted that at this time the lower end of the core assembly, that is, the electrode forming head 35 is located so that it can be guided in its downwardly movement by the ring.

It is the intent that there be effected a centering of the core assembly in coaxial relation to the shell even though in -the manual assembling of the parts they did not have to be in accurately centered relation. The ram and associated parts are lowered from the position shown in Fig. 2 with a powerful pressure necessary to distort the copper gasket but, ofcourse, not so powerful as to crush the ceramic body portion.k It is understood, of course, that the mechanism of the power press is organized so that the ram moves accurately in a straight line as indicated by the axis top 5I of the electrode setting gauge.

'I'he entire core assembly is thus lowered with a powerful force againstlthe resistance of the interposed soft metal gasket 32. This squeeze action has the effect of lowering the core assembly until the inner electrode is stopped by the fiat bearing surface 5I, thus accurately setting the electrodes in a plane flush with the bottom II. At this time the spark gap is accurately set by reason of the thickness of ring 50.

In so far as the gasket 32 is concerned, several results develop from this squeeze action. In the first place the gasket becomes distorted and elongates in its axial length so that there is more area of gasket contacting the core assembly and shell at the end of the operation (as in Figs. 1 and 3) than at the beginning. Another effect is that the gasket is otherwise deformed into such shape as may be imposed thereon by the surfaces engaging it, and the surfaces of the gasket both external and internal accurately assume the configuration of the surfaces bearing on the same. This squeeze action has another and important result. The ceramic body portion 2l is securely and permanently locked to the shell by reason of the gasket squeezed between the same so that the core assembly and the shell become an integral unit with the parts permanently fastened together in the position indicated in Figs. 1 and Y3.

It is the intent of this ldisclosure as illustrated in Fig. l, to bring the electrodes flush with the inner face C of the cylinder wall A. As this cylinder wall is of different thicknesses of material in different types of engines, itis necessary to provide spark plugs with spacing sleeves of different lengths as indicated in the previously filed application. Thls-means that the manufacturer must maintain in stock spacing rings, one of which is shown at 2l, of variable lengths to compensate for variations in the thickness of material in the different engine heads.

In assembling the spark plug parts, as illustrated in Fig. 3, that length of spacing sleeve necessary for the instant situation, giving due consideration to the thickness of the usual washer 22, is selected from stock and inserted loosely on the threaded end of the unit formed from the Fig. 2 operation. The spacing sleeve is then forced on to the shell and the insulating sleeve locked to the shell by means of the apparatus disclosed in Fig. 3. There is shown a power press which includes a lower die 55 provided centrally thereof with a Arecess 5i having a diameter to receive therein the lower threaded end of the spark plug unit received from the Fig. 2 operation. The unit with the proper length of spacing sleeve 2| is inserted in place with the spacing sleeve initially resting on the upper bearing surface 58.01e the lower die. vThe 'insulated sleeve is inserted into the lower end of the shielding barrel if not already there as above indicated, and the barrel mounted with its lower or bushing forming end intruding into the upper portion of the shell and bearing on the harige 30. In this initial assembling, it is not necessary that the parts'be accurately disposed in their coaxial position for the press will automatically insure the proper axial disposition of the parts. l

The upper die 5S of the press is then lowered to receive the upper portion of the lined barrel in a recess SII provided therefor. The upper die is lowered until its fianging lower portion 6I engages and bears against the upstanding flange I1 of the spark plug shown in Fig. 2 to bend, or roll or curve this flange inwardly into bearing engagement with the bevelled bearing shoulder 46 at the bottom of the shielding barrel. At the same time. the squeeze action of the die press forces the spacing sleeve 2| in snug engagement with the cylindrical bearing portion sliding the same along this portion until the sleeve engages against and firmly bears againstthe shoulder I8. The Darts of the spark plug thus formed are then removed from the parts of the press shown in Fig. 3 and the spark plug thus formed is ready to receive the current supplying cable or harness forming no part of this disclosure. l

It is appreciated that as the barrel I4 -is forced downwardly into engagement with the shoulder cf the body portion, the barrel in effect'takes the place of the plunger53 so that the barrel Will likewise be fixed co'ncentric to the axis a-b. It will also be appreciated that as the barrel is forced downwardly it will bring its lining 43 into engagement with the shoulder 30 and the shoulder will react on the lining to locate the same in firm engagement with the stop flange 42 at the top of the barrel. It is thus seen that all of the parts are accurately located in their final intended position mechanically, that is, by the mechanical action of the presses and independent of any carelessness of the unskilled operator in initially assembling the component parts.

It is also suggested that means be provided to restrain any rotation of the shielding barrel I4 in the shell I2 incidental to the screwing on to the threads at Ill of the usual current supplying cable which engages the upper end of the spindle. As shown in Fig. 4 this resistance to rotation is attained by providing a straight knurl 62 which projects from the shell into the otherwise cylindrlcal upper portion 24 of its bore. The shell being of steel and the barrel I6 being of brass, the forcing of the barrel axially into place in the Fig. 3 operation causes the burrs on the knurl to out grooves in the brass. This will form a keyed interlock between the barrel and shell suiicient to re,- sist relative rotary movement between them.

The spark plug is mounted in the opening B of the engine following conventional practices.

locating the washer 22 in place and screwing the plug snugly in position by a Wrench engaging the hex portion I6 with incidentalV squeezing of washer 22 to avoid any possibility of leakage at the top of the threaded portion.

I claim:

l. A shielded spark plug comprising a shell having a long conical gasket seat. a core assembly having its lower portion of conical form, a soft metal gasket of conical form engaging said seat and squeezed between the seat and said conical portion of the core assembly to lock the core `as sembly to the shell, said core assembly provided Amid-height With an outstanding shoulder, a

shielding barrel lined with an insulating tube telescoping the upper portion of the core assembly and projecting above the same to form a pocket for receiving a conductor leading to the top of the core assembly, said barrel provided at its lower endfwith an outstanding flange having its underside 1contoured to fit on said shoulder and the upper end of the shell rolled over into bearing engagement with the flange to force the core assembly into position to squeeze the gasket on to its seat with incidental distortion of the soft metal gasket from its initial configuration.

2. A shielded spark plug including a shell, a

l andere core assembly'intruded in the shell and provided with an upwardly facing shoulder, a gasket squeezed between the core assembly and shell, a shielding barrel having its lower end intruded into the upper portion oi' the shell, bearing on the shoulder and provided with a bore extending axially therethrough, said barrel provided at its upper end with a stop flange projecting into lthe bore and the bore being otherwise of uniform diameter from end to end and a tube of insulating material lining inserted into the lower open end of the bore with the upper endof the lining engaging said stop flange and the lower end engaging said shoulder and the upper end of thek shell bent inwardly into hearing engagement with the barrel to forcethe same into engagement with said shoulder and said shoulder reacting on the insulation tube to hold the same clamped between the shoulder and the stop flange.

3. In la spark plug, the combination of a shell provided with a bore extending axially therethrough, the upper portion of the bore being enlarged and the portion therebelow being frustoconical and yproviding a long gasket seat with its larger end uppermost, a core assembly provided midlength with an outstanding annular flange located in the enlarged upper portion of the bore and therebelow being of frusto-conlcai form,- a soft metal gasket snugly fitting between the seat and said frusto-conical part of the core assembly, and spacing the assembly from the shell, a metallic shielding barrel containing the upper part of the core assembly and provided at its lower end with an outstanding bushing directly bearing on top of the flange and the'upper portion of the shell rolled over into bearing engagement with said bushing.

4. In a spark plug, the combination of a shell provided with a bore extending axially therethrough, the upper portion of the bore being enlarged and the portion therebelow being frustoconical and providing a, long gasket seat with its larger end uppermost, a core assembly provided with an outstanding annular flange located in the enlarged upper portion of the bore and therebelow being of frusto-conical form, a soft metal gasket snugly .fitting between the seat and said frusto-conical part of the core assembly, and spacing the assembly from the shell, a metallic shielding barrel containing the upper 'part of the core assembly and engaging said flange, and cooperative means on said shell and said barrel for securing them together. v

LEWIS F. HAHN.

REFERENCES @man x'Ihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,126,975 Furber Feb. 2, 1915 1,241,562 Schmidt Oct. 2, 191'? 1,819,692 Shapiro Aug. 18, 1931 1,823,430 Rabezzana Sept. 15, 1931 1,835,574 Rabezzana Dec. 8, 1931 1,929,202 Hahn Oct. 3, 1933 1,979,856 Bennett Nov. 6j 1934 2,003,464 Rabezzana' June 4, 1935 2,008,803 Stephan July 23, 1935 2,026,822 Close Jan. '1, 1936 y 2,041,136 Klingner May 19, 1936 2,064,089 Stemmeler Dec. 15, 1936 2,109,029 Nowosielski Feb. 22, 1938 2,150,500 Graf Mar. 14, 1939 2,150,723/ Nowosielski Mar. 14, 1939 2,198,892 Twining Apr. 30, 1940 2,272,882 Brown Feb. 10, 1942 2,308,968 Gregory Jan. 19, 1943 2,336,569 Rabezzana Dec, 14,1943 2,356,104 Tognola Aug, 15, 1944 2,400,318 Rosan May 14, 1946 FOREIGN PATENTS Number Country Date 3,715 Great Britain Mar. 9, 1915 

